1. Field of the Invention
The present invention relates to a zinc oxide nanorod thin film and a method for making the zinc oxide nanorod thin film.
2. Description of the Prior Art
Zinc oxide is a direct-bandgap semiconductor having ideal photoelectric properties, including a bandgap of 3.37 eV at room temperature with significant exciton binding energy (60 meV) and high refractive index (n=2.01 for 550 nm). Therefore, zinc oxide may be widely used in making light-emitting diodes (LED) and solar cells.
Conventional methods for making the zinc oxide nanorod thin film are complex and expensive. These conventional methods include: chemical vapor deposition, laser ablation, sputtering and sol-gel spin coating. Practicing such methods requires a vacuum and high-temperature, which is extremely expensive and unfavorably raises costs. Thus seeking a non-vacuum, low-temperature, low-cost and simple method is highly relevant.
Vayssieres et al. has proposed a conventional low-temperature solution growing method (J. Phys. Chem. B 2001, 105, 3350) for making zinc oxide nanorod thin films. However, a zinc oxide nanorod thin film made with the conventional method proposed by Vayssieres et al. has many holes left unfilled between hexagonal prismatic zinc oxide nanorods of which the zinc oxide nanorod thin film is made.
In additional to the aforementioned conventional low-temperature solution growing method, Tak et al. disclosed physical properties of zinc oxide nanorod thin films made with conventional methods (J. Phys. Chem. B 2005, 109, 19263). According to the prior art, through altering growing factors, such as, pH of growing solution, growing temperature, properties of a seed layer, or zinc ion concentration, proportionate changes are made to properties of the zinc oxide nanorod thin film. However, simply altering growing factors does not provide a highly condensed zinc oxide nanorod thin film of ideal photoelectric properties having a packing density over 0.84.
A conventional method for making a nanorod thin film disclosed in U.S. published application no. 2007/0220713 A1 also fails to provide a highly condensed nanorod thin film, so establishing a long-felt and unsolved need for highly condensed zinc oxide nanorod thin film of ideal photoelectric properties.
It is significant that the prior art fails to provide a highly condensed zinc oxide nanorod thin film of ideal photoelectric properties due to various problems, especially, existence of unfilled holes between nanorods. To overcome the shortcomings, the present invention provides a zinc oxide nanorod thin film and a method to make the same to mitigate or obviate the aforementioned problems.